1. Field of the Invention
The invention relates to a method for controlling an electrical drive of an electrically driven compressed air compressor of a motor vehicle and a corresponding control circuit.
2. Description of the Related Art
It is known from practice to provide compressed air compressors, so-called air compressors, to supply pneumatic braking systems in commercial vehicles, wherein said air compressors function according to the reciprocating piston principle. Depending upon the application purpose, it is necessary to provide for hybrid-electrical commercial vehicles, in other words commercial vehicles that are equipped with a hybridized drive train, air compressors that are driven at least in part in an electrical manner, said air compressors also being referred to in short as “e-AC”. The electrical drive of an electrically driven compressed air compressor can comprise a frequency converter and an electric motor, wherein the electric motor can be embodied as an asynchronous machine, synchronous machine, or a reluctance machine.
However, air compressors that are based in particular on the reciprocating piston technique have load torques that have high peaks and non-linear fluctuations for which the electrical drive must compensate. Even in the case of constant pressure loadings at the air compressor outlet connection, the torque changes greatly in a non-linear manner during a full rotation of the crank shaft. This leads to high power losses, especially in continuous operation. Further disadvantages are represented by the required high magnitude of electrical energy reserve, in particular for starting the motor of the air compressor, and the high cooling requirements, for example in the case of a slow motor start-up in the presence of a high torque of an air-cooled asynchronous machine. This leads to greater expenditure and higher costs relating to the performance electronics and the motor, for example in relation to the thermal behaviour and current capability.